The present invention relates to clutch controls for automatically controlling the engagement and disengagement of transmission master clutches, and more particularly relates to clutch controls for master clutches utilized with mechanical transmissions, in particular with automatic mechanical transmission systems, which simulate the current clutch operating surface temperatures and automatically operate the clutch in response to a simulated temperature greater than a predetermined limit.
Automatic mechanical transmission systems and the automatic controls for the master clutches thereof are known in the prior art as may be seen by reference to U.S. Pat. Nos. 3,478,851; 3,752,284; 4,019,614; 4,038,889; 4,081,065 and 4,361,061, the disclosures of which are hereby incorporated by reference.
Briefly, in such automatic mechanical transmissions systems, various drive line operations include the supply of fuel to the engine, the engagement and disengagement of the master clutch, the shifting of the transmission and the operation of other devices such as input or output shaft brakes are automatically controlled by a control system, including a central processing unit, based upon certain measured, sensed and/or calculated input parameters. Typically, the input parameters include engine speed, throttle position, transmission input and/or output shaft speed, vehicle speed, current engaged gear ratio, application of the brakes and the like. The term throttle position is utilized to signify the position or setting of any operator controlled device for controlling the supply of fuel to an engine.
Referring specifically to the automatic clutch control, in a vehicle equipped with an automatic mechanical transmission, during normal operation, when starting from at rest or operating at a very low speed, the master friction clutch is modulated between fully disengaged and fully engaged conditions, i.e. is partially engaged, according to certain input parameters, to maintain the engine speed at a set value above idle speed and/or to achieve smooth starts. Typically, the set value is throttle position modulated to provide appropriate starting torque and the clutch is moved toward engagement and disengagement, respectively, as the engine speed increases above and falls below, respectively, the set value.
In another system, as described in U.S. Pat. No. 4,081,065, the clutch is modulated in accordance with throttle position, engine speed and engine acceleration.
While the above automatic mechanical transmission systems are considered to be highly advantageous, they are not totally satisfactory as, in certain start up conditions when the vehicle does not have sufficient torque in the selected gear to move the vehicle load or the vehicle does not have sufficient traction to move the load, the operator may allow the clutch to remain in the partially engaged (i.e. slipping) position for an excessive period of time which may result in excessive heat buildup in the clutch and damage thereto. Such conditions can occur in starts up a steep grade and/or in mud, sand or snow.
Clutch control systems utilizing temperature sensors, such as bi-metalic reed devices and the like, located in the clutch are known in the prior art as may be seen by reference to U.S. Pat. Nos. 4,072,220 and 4,199,048, the disclosures of which are hereby incorporated by reference. Automatic clutch controls having means to simulate heat buildup by monitoring throttle position and slip are known as may be seen by reference to above-mentioned U.S. Pat. No. 4,081,065.
In another automated clutch control system, as described in U.S. Pat. No. 4,576,263, the clutch is modulated in accordance with throttle position, engine speed and engine acceleration by simulating clutch temperature utilizing sensed and/or calculated inputs.
The prior art systems for monitoring and/or simulating clutch temperature to prevent heat related damage thereto are not totally satisfactory as the systems did not provide adequate automatic response to sensed conditions. They also did not interact with related automatic mechanical transmission system parameters. They often utilized relatively complicated, unreliable and/or expensive sensors which were difficult and/or expensive to produce, assemble and/or maintain. Further, the prior art systems did not measure temperature at the operating (i.e. friction) surfaces or simulate clutch heating and clutch cooling conditions to accurately simulate current clutch temperature and/or based each temperature simulation from a fixed starting point not related to a constantly maintained current temperature simulation.
In accordance with the present invention, the drawbacks of prior art have been overcome or minimized by providing a heat dissipation prediction method of controlling heat buildup in the clutch to protect the clutch from excessive wear and/or damage resulting from heat buildup at the friction surfaces during excessively long and/or repeated clutch slipping operations. Such undesireable clutch slipping operations can be caused to occur by inexperienced, unskilled and/or inattentive operator attempts to start the vehicle under unsuitable traction conditions, attempting to start the vehicle with insufficient torque in the selected gear ratio (often associated with attempting to start a heavy loaded vehicle up a steep grade) and/or driver riding the throttle to maintain a vehicle stationary on a hill.
The heat dissipation prediction method comprises the steps of determining a heat buildup value based on an engine operating parameter, comparing the heat buildup value with a first predetermined heat buildup limit, comparing the heat buildup value with a second predetermined heat buildup limit, and setting an operating mode of the clutch based on the heat buildup value.
The heat buildup value will be increased or decreased based on comparing the various operating parameters with a baseline threshold and a baseline slip. The clutch will be caused to engage more rapidly in an aggressive mode of operation to cease slip related heat buildup when the heat buildup value is greater than a first predetermined heat buildup limit. When the heat buildup value exceeds a second predetermined heat buildup limit and the vehicle speed is slow, the clutch will be caused to rapidly disengage in a fully disengage mode of operation. Thus, the clutch will be caused to become fully disengaged or more rapidly engaged based on the heat buildup value.
Accordingly, it is an intent of the present invention to provide an automatic clutch control system for determining a heat buildup value from sensed and/or calculated inputs and for operating the clutch to minimize or prevent excessive wear and/or damage thereto resulting from slip related temperature buildup.
Various additional aspects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.